1. Technical Field
The present invention relates to a development roller having a roughness on the circumference thereof for transporting toner to a latent image bearing unit, a development device containing the development roller, an image forming apparatus containing the development device, and a method of manufacturing the development roller.
2. Related Art
Development devices developing a toner image from a latent image with one-component non-magnetic toner triboelectrically charge the toner on a development roller. A development roller known in the related art (such as the one disclosed in Japanese Unexamined Patent Application Publication No. JP-A-2007-121948) has a surface roughness on the circumference thereof, the roughness having a substantially flat top surface. With the surface roughness, the development roller triboelectrically charges the toner thereon. As illustrated in FIG. 10A, a development roller a includes a base unit b and a surface layer c plated on the base unit b as a coverage.
The development roller a generally remains in contact with a toner feed roller and a toner regulator (both not shown). Silica having a high hardness is used serving as an external additive that coats toner mother particles of the toner. A roughness portion, composed of a plurality of recesses d and projections e, is formed on the circumference of the base unit b. A roughness portion, composed of a plurality of recesses f and projections g, is formed on the circumference of the surface layer c.
The surface layer c is worn by the toner feed roller and the toner regulator in an image forming operation. A demand for high-quality image and reduction in toner consumption is mounting today. The particle diameter of the toner currently becomes smaller. If the image forming operation has been performed with the small particle size toner for a long period of time, the surface of the top portion h of the projection g is relatively heavily worn in a generally flat configuration while the surface of the recess f is generally unworn as illustrated in FIG. 10B. If the degree of wear is different from the recess f to the projection g, the depth of the roughness portion is reduced in the long service life of image forming of the development roller. The amount of toner transported by the development roller is thus reduced. It becomes difficult to maintain the image density level of each image and to continue the development process for a long period of time.